The research proposed here will examine the molecular basis of synaptic plasticity at electrotonic and glutamatergic synapses in the retina. SpecificaUy, the biophysical properties and molecular structures of the gap junction channels and glutamate receptors of teleost retinal horizontal cells will be characterized with particular attention to the mechanisms by which these synaptic membrane channels are modulated by the dopaminergic interplexiform system. This research will provide information on the molecular events during the first steps of visual information processing in the eye, and has broad implications for understanding the molecular basis of synaptic modulation in the central nervous system. In this regard it is potentiahy useful in ameliorating dysfunction of other brain dopaminergic systems, such as occurs in Parkinsonism and schizophrenia, and in understanding the role of glutamate receptors in neurodegenerative cell death and in learning and memory. Experiments will be conducted using retinal neurons isolated from the zebrafish (Brachydanio rerio). The biophysical properties of horizontal cell gap junction and glutamate-receptor channels will by described using patch and whole cell voltage clamp recordings from dissociated cells. The modulatory effects of dopamine on these channels will also be characterized. In addition, the action of other potential modulatory transmitters such as melatonin and VIP, and other intracellular messengers such as cGMP and PKC will be examined. The molecular structure of these ion channels will be elucidated by cloning of their respective cDNAs from a zebrafish cDNA library. Fragments of these genes will be obtained by PCR amplification of zebrafish DNA with primers designed by analysis of homologous mammalian genes. The retinally expressed fragments will be identified by Northern blotting, and then used to obtain full-length cDNAs. The resulting clones will be characterized as to their cell-specific expression by in situ hybridization, subcellular localization of their gene products by immunocytochemistry, and functional expression as channel proteins by expression in oocytes. Structure-function models of these channels reflecting these biophysical and molecular studies win then be produced.